Arrow Flow Animation
Array + Curve modifiers should make it work:


In Edit mode make sure that the curve direction is good, if not press W > Switch Direction.
Put the origin of the curve at its beginning point.
Put the arrow object at the same point.
Give your arrow an Array modifier with as many Count as you want and choose the Offset (distance between the arrows).
Give your arrow a Curve modifier, choose the Curve as Object, and choose the right Deformation Axis.
Move the arrow along the X or Y axis, depending on the orientation of the curve on the scene.